Modular Properties of Generalised Gibbs Ensembles: The Deformed KdV Hierarchy
Abstract
We construct a set of conserved charges which are deformations of quantum KdV charges. They are associated with the modular transformation of a GGE with the spin-σ KdV charge inserted with chemical potential ασ. The charges are formal power series in the chemical potential, with coefficients given by local integrals of motion. We define local recursion relations and equivalent flow equations, prove commutativity to all orders, and establish uniqueness of the currents modulo total derivatives for a fixed generating series. We show that the eigenvalues of these deformed charges can be obtained from the thermodynamic Bethe Ansatz in two models. In the c=1/2 free fermion theory, the deformed charges reduce to explicit linear combinations of undeformed KdV charges, and their ground-state eigenvalues agree with the TBA expansion to all orders. In the Lee-Yang model, we find numerical agreement through cubic order in the spin-$5$ deformation for the first few charges evaluated on low-lying states.
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BibTeX
@misc{karimi2026modular,
title = {{Modular Properties of Generalised Gibbs Ensembles: The Deformed KdV Hierarchy}},
author = {Faisal Karimi},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.13875},
eprint = {2610.13875},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.13875},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Modular Properties of Generalised Gibbs Ensembles: The Deformed KdV Hierarchy
AU - Faisal Karimi
PY - 2026
DA - 2026/10/09
PB - arXiv
DO - 10.48550/arxiv.2610.13875
UR - https://arxiv.org/abs/2610.13875
AB - We construct a set of conserved charges which are deformations of quantum KdV charges. They are associated with the modular transformation of a GGE with the spin-σ KdV charge inserted with chemical potential α_σ. The charges are formal power series in the chemical potential, with coefficients given by local integrals of motion. We define local recursion relations and equivalent flow equations, prove commutativity to all orders, and establish uniqueness of the currents modulo total derivatives for a fixed generating series. We show that the eigenvalues of these deformed charges can be obtained from the thermodynamic Bethe Ansatz in two models. In the c=1/2 free fermion theory, the deformed charges reduce to explicit linear combinations of undeformed KdV charges, and their ground-state eigenvalues agree with the TBA expansion to all orders. In the Lee-Yang model, we find numerical agreement through cubic order in the spin-$5$ deformation for the first few charges evaluated on low-lying states.
ER -